Otter Predation onTaricha granulosaand Variation in Tetrodotoxin Levels with Elevation

Abstract

Tetrodotoxin (TTX) is a low molecular weight neurotoxin that is found in a wide variety of taxa. Tetrodotoxin blocks voltage-gated sodium channels, preventing the propagation of action potentials and inducing paralysis in susceptible animals. Taricha granulosa have been documented to possess TTX in high quantities and are preyed upon by snakes of the genus Thamnophis. However, recent observations of predation events on T. granulosa by otters were documented in a high-elevation population just outside of Crater Lake National Park, Oregon. We quantified TTX levels in this population as well as 3 populations in Crater Lake National Park using a Competitive Inhibition Enzymatic Immunoassay. We further compared these high elevation populations to a known high-toxicity population from Benton County, Oregon. We found that the populations in Crater Lake have lower levels of TTX relative to populations outside of the lake, and that all high-elevation locations have relatively low levels of TTX. We then analyzed previously published whole-newt TTX levels and elevation, and found that there is a significant negative relationship. However, there is a non-significant relationship between whole-newt TTX levels and elevation when examining elevations below 500 m. This further exemplifies the potential for novel predation and previously unidentified selective pressures in high-elevation newt populations.